Abstract
Bio-insecticides have been increasingly used worldwide as ecofriendly alternatives to pesticides, but data on their effects in non-target freshwater organisms is still scarce and limited to insects. The aim of this study was to determine the lethal and sub-lethal effects of the bio-insecticides Bac Control (based on Bacillus thuringiensis kurstaki-Btk) and Boveril (based on Beauveria bassiana-Bb) on regeneration, behavioral, and reproductive endpoints of the freshwater planarian Girardia tigrina. The estimated LC50-48h were > 800 mg a.i./L for Btk and 60.74 mg a.i./L for Bb. In addition, exposure to Btk significantly decreased locomotion and feeding activities of planarians (lowest observed effect concentration (LOEC) of 12.5 mg a.i./L Btk) and fecundity rate (LOEC = 3.12 mg a.i./L Btk), whereas exposure to Bb significantly delayed regeneration (LOEC = 0.75 mg a.i./L Bb) and decreased fecundity rate (1.5 mg a.i./L Bb) of planarians. Thus, both bio-insecticides induced deleterious sub-lethal effects on a non-insect freshwater invertebrate species. However, only Bb-based formulation affected the survival, fecundity rate, and regeneration at concentrations below the maximum predicted environmental concentration (PEC = 247 mg/L). Thus, care should be taken when using such formulations as alternatives to chemical insecticides near aquatic ecosystems.
Highlights
Bio-insecticides have been increasingly used since the 80’s as alternatives to reduce the impacts on the environment and public health posed by application of chemical insecticides for the control of pests (Gupta and Dikshit 2010; Singh et al 2018; Vivekanandhan et al 2018)
Locomotor velocity was significantly decreased in planarians exposed to Bacillus thuringiensis kurstaki (Btk) with a LOEC of 12.5 mg a.i/L (F (5,66) = 13.17, p < 0.0001, Figure 1a)
This shows that adults of G. tigrina, a non-target and non-insect species, seem to be very sensitive to formulations based on Beauveria bassiana (Bb), but not so sensitive for Btk when compared to chironomids, Daphnia magna, the frog Leptodactylus latrans, and zebrafish (Table 1)
Summary
Bio-insecticides have been increasingly used since the 80’s as alternatives to reduce the impacts on the environment and public health posed by application of chemical insecticides for the control of pests (Gupta and Dikshit 2010; Singh et al 2018; Vivekanandhan et al 2018) These biological compounds are based on microorganisms (bacteria, fungi, virus or protozoa) and have been considered ecofriendly due to their specificity, low toxicity, fast decomposition and efficacy when used in low concentrations (Gupta and Dikshit 2010; Kandpal 2014; EPA 2016). Strains of Bacillus thuringiensis occupied prime position in biopesticide’ market followed by entomopathogenic fungi, such as Beauveria bassiana (Thakore 2006; Olson 2015; Subbanna et al 2019)
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